Well, after the excellent info on 'normal' soldering, I think it's time for users to weigh-in on their approaches and tools for surface-mount rework.I have recently entered into this world and can say for sure that it's annoying. I know with time that I will become more comfortable with it, but at the present time I dread having to go in there and fix stuff.Present needs range from 0402's to 144 pin LQFP.I note with no small irony that right as my eyes began to go, electronic components became nearly invisible.The upside is that if you drop a part, there is no point looking for it on the floor...............
Neither threat nor menace. Think of it as an opportunity. It is also the way of the world.
Tools you need, in no particular order (because you need them all):
a) a good stereoscope. You can't solder what you can't see.
b) Metcal/OKI soldering tool with a range of tips. You're in the big leagues. You need tools. You don't skimp on microphones and you pay $$$ for fancy cable, so buy a real soldering station.
c) solder wick.
d) flux. You want flux. Flux is your friend.
e) bite the bullet and get the lead-free solder,as the parts you're buying and the boards you're re-working have lead-free pin finishes.
f) an assortment of tweezers and dental picks.
g) hot-air rework station with an assortment of nozzles.
h) a proper low-foaming cleaner like Detergent 8 (that's what it's called), diluted as necessary. Because with all of that flux, you'll have to clean the board.
i) stiff brush to clean the flux.
j) supply of deionized/distilled water for rinsing.
k) shop air to blow the boards dry after rinsing.
l) Solder paste, if you're adventurous.
m) those little quarter-size things of tip tinner are nice.
Soldering QFPs and SOICs is not that tough. Align the package. Tack-solder the corner pins. Apply flux, then "drag solder" all of the pins. You'll make a mess and the solder will blob over more than one pin. Get your thin solder wick and clean it up.
Soldering passives is likewise easy. Do not tin the pad, but do put down some flux. This prevents tombstoning. Get some solder on the iron tip. Hold the part down with your tweezers while you touch the tip to the pad and to the end of the part. Let the solder flow. Do the other side of the part.
Need to remove an SMD chip or passive? Get out the hot-air tool. Select the right nozzle. Use the lowest velocity air and let it get hot. The idea is to get the air hot enough to melt the solder (which happens at what, 200C?) while not scorching the board and lifting up pads. Let the tool heat up the work while you poke underneath the chip with a dental pick or tweezers. When it's right, the solder will suddenly flow and the part will flow up, so flip it up/grab it with the tweezers and remove the air. Then grab your soldering iron, solder wick and some flux and clean up the pads.
Most people don't know this, but MLC ceramic capacitors were not designed for hand soldering. They're actually pretty easy to break. The big/wide parts (those great 10 uF parts used in switch-mode power supplies) are the worst for this. They tend to break if you have some solder on the pad before you put the part down and you then press on the part while soldering.
After soldering, clean the board. Spritz the detergent onto the board and scrub the flux off with your brush. Hint: a narrow painting "chip" brush, with all but about 3/16" of the bristles cut off, is a fabulous PCB scrub tool. Then rinse with the deionized water. Shop air from the little pistol nozzle at about 30 psi is great for blowing out the excess water. The detergent and using DI water make this easy, because the water tends to collect like water on a newly waxed car, and it just blows out.
Obviously, unsealed pots and switches aren't washable, so put them on last after assembly. If you're doing rework, then do your best to keep the cleaning agents and flux out of them.
Don't be scared of SMT. Impress your friends with your mad rework skills!